Method of and apparatus for optical sensing of media through a suction or mesh belt

ABSTRACT

An optical sensing assembly ( 20 ) detects media ( 32 ) carried by a traveling mesh or suction belt ( 34 ) having material portions ( 82 ) that define therebetween open portions ( 84 ). An emitter ( 22 ) is disposed opposite and spaced apart from the first side of the belt ( 34 ). The emitter ( 22 ) emits light in a direction from the first side toward the second side of the belt ( 34 ). A detector ( 24 ) is disposed opposite and spaced apart from the second side of the belt ( 34 ) and generally opposite the emitter ( 22 ). A portion of the light emitted by the emitter ( 22 ) passes through the open portions ( 84 ) of the mesh belt ( 34 ) and impinges upon the detector ( 24 ). The detector ( 24 ) issues a detect signal (DET_SIG) indicative of a reduction in the detected portion of light. The detect signal (DET_SIG) is filtered to reject reductions in the detected portion of light that are not due to the presence of media ( 32 ) on the belt ( 34 ).

FIELD OF THE INVENTION

The present invention relates generally to electrophotographic printing and/or copying machines and, more particularly, to such machines having a media-carrying conveyor belt of the suction or mesh type.

BACKGROUND OF THE INVENTION

The process of electrophotography involves forming an electrostatic charge pattern on a dielectric surface, such as the surface of a photoconductive recording element, creating a latent image to which charged toner particles are attracted. The toner image is, in turn, transferred onto an image-receiving media, such as, for example, a piece of paper, that is brought or carried into contact with the dielectric surface.

The imaged media is typically carried by a conveyor belt into a fusing station having a heating device that applies heat to the media and thereby fixes or fuses the toner to the media. The conveyor belt may be configured as a suction or mesh belt. Suction or mesh belts are constructed of a porous or mesh material, such as, for example, a loose-weave fabric or metal mesh belt. One or more fans or other air-moving devices disposed below the belt are configured to draw air through the porous or mesh belt thereby creating a partial vacuum that holds the media in place on the moving conveyor belt.

For proper operation of the electrophotographic printing or copying machine, it is necessary to sense the presence and/or absence of media on the conveyor belt. More particularly, it is necessary to accurately infer the position of the leading and/or trailing edge of the media. Reflective-type optical sensors have been used for this purpose. However, the reflectance or reflection density of the typical types of media (imaged and non-imaged) used in the printing or copying machines varies substantially, and thus makes reliable detection of media using reflective-type optical sensors problematic. More particularly, the reflection densities of a piece of paper and an image on a piece of paper can overlap substantially with the reflection density of a loose-weave or mesh conveyor belt of the machine.

As an example of this overlap, the reflection density of a bare piece of paper is typically from approximately 0.04 to approximately 0.1 units, a full image on the piece of paper can increase the reflection density up to approximately 2.0 units, and the reflectance of the loose-weave fabric belt can be from approximately 0.04 to 2.0 units. This substantial variation in and overlap of the reflection densities of the media and the conveyor belt render it difficult at best to distinguish between the media and the belt, and thereby makes it difficult to repeatably and reliably detect the media with a reflective-type sensor.

Therefore, what is needed in the art is a method and apparatus for optically sensing media traveling upon a loose-weave fabric or mesh belt.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for optically detecting the presence and/or absence of media being carried upon a traveling mesh or suction belt.

The invention includes, in one form thereof, an emitter disposed opposite and spaced apart from the first side of the belt. The emitter emits light in a direction from the first side toward the second side of the belt. A detector is disposed opposite and spaced apart from the second side of the belt and generally opposite the emitter. A portion of the light emitted by the emitter passes through the open portions of the mesh belt and impinges upon the detector. The detector issues a detect signal indicative of a reduction in the detected portion of light. The detect signal is filtered to reject reductions in the detected portion of light that are not due to the presence of media on the belt.

An advantage of the present invention is that a transmissive, rather than reflective, detecting/sensing device is used.

Yet another advantage of the present invention is that the substantial variation in and overlap of the reflection densities of various media types do not substantially impact the reliability of the detecting/sensing device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become apparent and be better understood by reference to the following description of one embodiment of the invention in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic representation of an electrophotographic printing and/or copying machine having one embodiment of an apparatus for the optical sensing of media through a suction or mesh belt of the present invention;

FIG. 2 is a partially longitudinally cross-sectional view of the belt, transport mechanism and optical sensor assembly of FIG. 1;

FIG. 3 is a detail view of a portion of the belt of FIGS. 1 and 2;

FIG. 4 a illustrates an exemplary irradiance pattern of a non-lens-type emitter;

FIG. 4 b illustrates an exemplary irradiance pattern of a lens-type emitter; and

FIGS. 5 and 6 show the electronic signals issued by the optical sensor assembly of FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, there is shown an electrophotographic printing and/or copying machine that includes one embodiment of an apparatus for the optical sensing of media through a suction or mesh belt of the present invention.

Electrophotographic printing and/or copying machine 10 (hereinafter referred to as machine 10) includes fuser transport assembly 12. Machine 10 and fuser transport assembly 12 are generally similar to the electrophotographic printing and/or copying machine that is described in co-pending U.S. Patent Application Serial No. 2002/0139264, filed 18 Dec. 2001 and published on 3 Oct. 2002, and which is entitled DIGITAL PRINTER OR COPIER MACHINE, the disclosure of which is incorporated herein by reference. Therefore, many of the structural and operational details of machine 10 and fuser transport assembly 12 are not reproduced at length herein. Rather, only the structural and operational details of machine 10 and fuser transport assembly 12 that are relevant to the present invention are discussed.

As shown in FIG. 1, machine 10 includes optical sensing assembly 20, which includes emitter 22, detector 24, controller 26, driver 28 and filter 30. As is described more particularly hereinafter, optical sensing assembly 20 senses or detects the presence and/or absence of media 32, such as, for example, a piece of paper or vellum, through suction or mesh belt 34. Thus, optical sensing assembly 20 detects the presence and/or absence of media on belt 34 by transmissive means, i.e., by detecting light that has been transmitted or passed through belt 34, rather than by reflective means. The use of transmissive instead of reflective detection renders optical sensing assembly 20 substantially less sensitive to the varying reflectance of various types of media. Therefore, optical sensing assembly 20 more reliably detects various types of media when compared to conventional reflective detection.

Emitter 22 is disposed a predetermined distance above or apart from a first or media-carrying side of belt 34, and emits light that is directed from the top/media side of belt 34 toward the bottom/non-media side thereof. Emitter 22 is configured as a light emitting diode or infrared light emitting diode, such as, for example, a gallium aluminum arsenide hermetic infrared light emitting diode. Commercially available versions of such a diode suitable for use as emitter 22 include OP231W and OP232W manufactured by OPTEK Technologies, Inc., of Carrolton, Tex. Emitter 22 preferably has a broad irradiance pattern and provides relatively even illumination over a broad area. Emitter 22 includes an emitter input 36. The amount of light emitted by emitter 22 is dependent at least in part upon the level of the signal applied to emitter input 36.

Detector 24 is a light detecting unit, such as, for example, as a photodiode light detecting unit. Commercially available versions of detecting units suitable for use as detector 24 include the infrared photodiodes OPL820 and OPL821 also manufactured by OPTEK Technologies, Inc., of Carrolton, Tex. Detector 24 is disposed in general alignment with emitter 22. As will be more particularly described hereinafter, detector 24 is disposed such that belt 34 is intermediate detector 24 and emitter 22. Thus, detector 24 is disposed nearest, and is spaced a predetermined distance apart from, a second or non-media-carrying side of belt 34.

Detector 24 includes a light input 40 that admits light and a detector output 42. Detector 24 issues, on detector output 42, a detect signal DET_SIG that is active, such as, for example, a logic high voltage level, when the detector is not illuminated or when a predetermined and sufficiently low-level of light is impinging upon detector 24. Detect signal DET_SIG is otherwise inactive, such as, for example, a logic low voltage level, when a predetermined and sufficient level of light is impinging upon detector 24. Detector 24 includes Schmitt trigger-type circuitry that reduces noise and other falsely active conditions that otherwise might appear on detect signal DET_SIG due to high frequency transitions on light input 40.

Controller 26, such as, for example, a microprocessor, includes calibration input 44, controller input 46 and controller output 48. Calibration input 44 is electrically connected to detector output 42, and thus controller 26 receives detect signal DET_SIG. As will be more particularly described hereinafter, calibration input 44 is used during the calibration of optical sensing assembly 20. Controller input 46 is electrically connected to filter 30, and controller output 48 is electrically connected via driver 28 to emitter input 36. Controller 26 executes control and calibration software 50 that is stored in on-board memory (not shown) of controller 26 or in other memory (not shown), such as, for example, non-volatile memory for storing calibration data, accessible to controller 26. Controller 26 issues on controller output 48 a calibration signal CAL_SIG, the purpose of which will be more particularly described hereinafter.

Driver 28 includes a driver input 52 and a driver output 54. Driver input 52 is electrically connected to controller output 48, and thus driver 28 receives calibration signal CAL_SIG from controller 26. Driver output 54 is electrically connected to emitter input 36. Driver 28 issues, on driver output 54, emitter drive signal DRV_SIG, and, since driver output 54 is electrically connected to emitter input 36, emitter 22 receives emitter drive signal DRV_SIG. Emitter drive signal DRV_SIG is dependent at least in part upon calibration signal CAL_SIG issued by controller 26 and received by driver 28. The amount of light emitted by emitter 22 is dependent at least in part upon emitter drive signal DRV_SIG. Thus, the amount of light emitted by emitter 22 is dependent at least in part upon calibration signal CAL_SIG.

Filter 30 includes a filter input 62 and a filter output 64. Filter input 62 is electrically connected to detector output 42, and thus filter 30 receives media-indicating signal DET_SIG from detector 24. Filter output 64 is electrically connected to controller input 46. Filter 30 issues on filter output 64 media-indicating signal MED_SIG that is received on controller input 46 by controller 26. Media-indicating signal MED_SIG is active, such as, for example, a logic high level, when the presence of media is detected on belt 34 (i.e. detector 24 is not illuminated). More particularly, filter 30 is a digital filter that issues an active media-indicating signal MED_SIG in response to a predetermined number of sequential pulses occurring on detecting signal DET_SIG within a predetermined time period.

Belt 34, as best shown in FIG. 2, is suspended between and runs in direction B around shafts 72 and 74. More particularly, belt 34 is driven to run by drive shaft 74 and tensioned by tension shaft 72. Drive shaft 74 is driven to rotate by a motor (not shown). Belt 34 is constructed as an endless loop, preferably seamless, from a fabric, such as, for example, a woven, knit or mesh fabric or the like. As best shown in FIG. 3, the mesh structure of belt 34 includes material portions 82 that are spaced apart in a fairly regular and uniform manner and define therebetween open portions 84.

In use, and as best shown in FIG. 2, an emitter 22 and detector 24 pair are disposed in association with belt 34 such that emitter 22 is disposed a predetermined distance from the media-carrying side of belt 34 and detector 24 is disposed a predetermined distance from the non-media-carrying side thereof. The linear distance between emitter 22 and detector 24 is referred to as the separation distance SD. Separation distance SD is, for example, from approximately 0.1 inch to approximately 2.0 inches. However, separation distance SD is primarily determined by the electrical characteristics of the particular emitter 22 and detector 24 pair. The predetermined distance of the detector 24 from the belt 34 is appropriately one-third of the separation distance SD or less. Suction boxes 88 a and 88 b are disposed in association with belt 34 such that air is drawn through belt 34 in direction A from the media side toward the non-media side thereof.

Emitter 22 directs light through belt 34 towards detector 24. As belt 34 travels in direction B past detector 24 at a substantially uniform and known rate, the material portions 82 of belt 34 temporarily interrupt or significantly reduce the impingement of light beams upon detector 24 on a predictable periodic basis. This temporary interruption or reduction in the impingement of light beams upon detector 24 due to material portions 82 of belt 34 is best shown in FIGS. 4 a and 4 b.

FIG. 4 a shows emitter 22, configured as a point-type emitter having a broad irradiance pattern that relatively evenly illuminates a broad area. Material portion 82 is disposed between emitter 22 and detector 24, and thus temporarily interrupts or reduces the impingement of light beams L upon detector 24 as belt 34 travels past. Since the material portions 82 of belt 34 are spaced apart in a fairly regular and uniform manner, and since belt 34 is traveling at a known and substantially uniform rate, the reduction/interruption of light beams L occurs on a generally uniform periodic basis. Alternatively, as shown in FIG. 4 b, emitter 22 can also be configured as a lens-type emitter having a narrower and more focused irradiance pattern. The interruption of light beams L still occurs on a generally uniform periodic basis.

Using an emitter 22 having a broad irradiance pattern, as shown in FIG. 4 a, reduces the sensitivity of optical sensing assembly 20 to misalignment between emitter 22 and detector 24. Further, an emitter 22 having a broad irradiance pattern distributes the light intensity over a broad area so that the light diffuses through the media in such a way that even thin paper or vellum will block (or not transmit) enough light beams L to ensure reliable detection of most types of media.

Referring now to FIG. 5, the above-described signals issued by optical sensing assembly 20 during calibration and use are now discussed. As shown in FIG. 5, each time a material portion 82 of belt 34 passes between emitter 22 and detector 24, thereby interrupting or substantially reducing the level of light impinging upon detector 24, a pulse occurs on detect signal DET_SIG. The generally periodic pulses occurring on detect signal DET_SIG from time t₀ to time t₁ are due to material portions 82 of belt 34 interrupting or substantially reducing the level of light impinging upon detector 24, and are relatively short in duration. These relatively-short duration pulses occurring on detect signal DET_SIG are filtered out and/or rejected by filter 30 and thus media-indicating signal MED_SIG remains at an inactive, or logic low, state.

As belt 34 carries a sheet of media 32 between emitter 22 and detector 24, the interruption of and/or reduction in the impingement of light upon detector 24 occurs over a much longer duration relative to an interruption and/or reduction in the impingement of light upon detector 24 due to a material portion 82 of belt 34 moving between emitter 22 and detector 24. Thus, only when the level of light impinging upon detector 24 is interrupted or substantially reduced over a continuous and predetermined minimum period of time does filter 30 issue an active media-indicating signal MED_SIG indicating the presence of a sheet of media. This is illustrated at time t₁. When a piece of media carried by belt 34 is interposed between emitter 22 and detector 24 causing detect signal DET_SIG to become active for a relatively long duration. At time t₂, an active media-indicating signal MED_SIG is issued by filter 30.

Filter 30 delays issuing an active media-indicating signal MED_SIG from time t₁ to time t₂ to ensure that the interruption of and/or reduction in the impingement of light upon detector 24 is due to a piece of media 32 rather than one or more material portions 82 of belt 34 or other sources. The time between, or separating, time t₁ and time t₂ is identified in FIG. 5 and referred to hereinafter as time t_(FILTER). For example, with belt 34 traveling at a rate such that material portions 82 thereof block or substantially reduce the amount of light impinging upon detector 24 at a period of approximately every 2 milliseconds (mS). Filter 30 is configured, for example, with t_(FILTER) equal to 10 mS, i.e., as a 10 mS digital filter, and thus detect signal DET_SIG must remain active for at least 5 (five) consecutive periods of 2 mS, or for a total of at least 10 mS, before filter 30 issues an active media-indicating signal MED_SIG.

It is to be understood that the actual period of the pulses due to material portions 82 of belt 34 and the time period t_(FILTER) over which the detect signal DET_SIG must remain active for reliable detection of media 32 by optical sensing assembly 20 within a particular electrophotographic printing machine is relatively easily determined by one skilled in the art dependent at least in part upon the rate of travel of belt 34, the spacing between material portions 82 thereof, and the size of media 32 to be detected by optical sensing assembly 20.

As discussed above, the purpose of filter 30 is to distinguish between the relatively short-duration interruptions and/or reductions in the impingement of light upon detector 24 that are due to material portions 82 of belt 34 (also referred to as thread shadows) and the relatively long-duration interruptions and/or reductions in the impingement of light upon detector 24 that are due to media 32. The filtering process makes this distinction at least in part by issuing an active media-indicating signal MED_SIG only when a given interruption and/or reduction in the impingement of light upon detector 24 has a duration that is a predetermined amount of time greater than or a factor of the duration of a typical thread shadow. Thus, if the duration of a typical thread shadow is reduced, the time required by the filtering process (i.e., t_(FILTER)) to distinguish between thread and media shadows is also reduced. It is therefore advantageous to reduce and/or minimize the duration of the thread shadows.

By positioning detector 24 close to belt 34 the size, and thus the duration, of the thread shadows are reduced in much the same manner as the size of a person's shadow shrinks as he or she moves away from the light source and toward the surface upon which the shadow is being cast. Thus, by disposing emitter 22 at a substantial portion of the separation distance SD away from the media side of belt 34 and disposing detector 24 at the remaining relatively small portion of the separation distance SD from the non-media side of belt 34 the duration and size of the thread shadows is reduced. Preferably, detector 24 is positioned no further than one-third of the separation distance SD from belt 34. Most preferably, detector 24 is positioned as close as is practicable to the non-image side of belt 34 while emitter 22 is placed as far away from belt 34 as possible without exceeding the recommended or ideal separation distance between emitter 22 detector 24.

Calibration of optical sensing assembly 20 is performed by the execution of calibration software 50 in order to eliminate the occurrence of most, if not all, of the generally periodic pulses occurring on detect signal DET_SIG due to the passage of material portions 82 of belt 34 between emitter 22 and detector 24. Calibration software 50 sets the amount of light emitted by emitter 22 to a sufficiently high level that material portions 82 of belt 34 do not block or reduce the light impinging upon detector 24 by an amount sufficient to cause detector 24 to issue an active detect signal DET_SIG. The amount of light emitted by emitter 22 must not be set so low that detect signal DET_SIG is falsely made active. Thus, emitter drive signal DRV_SIG must be set to a level that corresponds to this desired amount of light output.

Emitter drive signal DRV_SIG is dependent at least in part upon calibration signal CAL_SIG issued by controller 26. Calibration software 50 adjusts the level of calibration signal CAL_SIG when no media is being carried upon belt 34 to ensure that detector 24 does not issue an active detect signal DET_SIG when material portions 82 of belt 34 pass between emitter 22 and detector 24.

More particularly, controller 26 receives on calibration input 44 detect signal DET_SIG. Calibration software 50 initially sets calibration signal CAL_SIG, and thereby emitter drive signal DRV_SIG, to a low level. Calibration software 50 gradually increases the level of calibration signal CAL_SIG, and thereby increases emitter drive signal DRV_SIG, until emitter 22 emits an amount of light that is sufficient to keep detector 24 illuminated at a level above the threshold of a detection event. Alternatively stated, the level of calibration signal CAL_SIG, and thereby the level of emitter drive signal DRV_SIG, are increased to a level where enough light is passing through mesh belt 34 and impinging upon detector 24 that detect signal DET_SIG remains inactive as material portions 82 of belt 34 pass between emitter 22 and detector 24. Thus, most if not all of the generally periodic pulses occurring between times time t₀ to time t₁ on detect signal DET_SIG prior to calibration of sensor assembly 20 (and shown in FIG. 5) are eliminated.

An exemplary detect signal DET_SIG occurring subsequent to the completion of the calibration process is shown in FIG. 6. Brief-duration pulses may nonetheless issue on detect signal DET_SIG as a result of, for example, events that are outside the parameters that existed during calibration and/or that exceed the safety margin and yet are not indicative of the presence of media between emitter 22 and detector 24. Such a pulse is shown occurring between times t₀ and t₁. As described above, filter 30 rejects such brief-duration “noise” pulses, and does not issue an active media indicating signal MED_SIG in response thereto. Rather, only at time t₂ when media is present between emitter 22 and detector 24 does filter 30 issue an active media indicating signal MED_SIG.

The level of calibration signal CAL_SIG is further increased a predetermined amount beyond or above the point where most if not all of the generally periodic pulses that occur due to the material portions 82 of belt 34 passing between emitter 22 and detector 24 by calibration software 50 to provide for a safety margin or a margin of error. Since the level of emitter drive signal DRV_SIG issued by driver 28 is dependent at least in part upon and/or is proportional to the level of calibration signal CAL_SIG, the light output of emitter 22 is thereby set to a level that prevents material portions 82 of belt 34 from blocking enough light to activate detect signal DET_SIG. Thus, reliable and repeatable detection of media by optical sensing assembly 20 is obtained.

In the embodiment shown, emitter 22 is disposed on the media-carrying side of belt 34 and detector 24 is disposed on the non-media-carrying side of belt 34. However, it is to be understood that the optical sensing assembly of the present invention can be alternately configured, such as, for example, with emitter 22 disposed on the non-media-carrying side and detector 24 disposed on the media-carrying side of belt 34.

In the embodiment shown, filter 30 is disclosed as a digital filter. However, it is to be understood that filter 30 can be alternately configured, such as, for example, as a software-based filter using known digital or analog filtering and/or debouncing algorithms.

In the embodiment shown, detect signal DET_SIG is connected to calibration input 44 of controller 26, and is therefore used during the calibration process and is read by calibration software 50. However, it is understood that controller 26 and calibration software 50 can be alternately configured to use media-indicating signal MED_SIG alone, or in conjunction with detect signal DET_SIG.

While this invention has been described as having a preferred embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Parts List

-   10. Electrophotographic Machine DET_SIG—Detect Signal -   12. Fuser Transport Assembly CAL_SIG—Calibration Signal -   20. Optical Sensing Assembly DRV_SIG—Drive Signal -   22. Emitter MED_SIG—Media Signal -   24. Detector -   26. Controller -   28. Driver -   30. Filter -   32. Media -   34. Belt -   36. Emitter Input -   38. Emitter Output -   40. Detector Light Input -   42. Detector Output Line -   44. Calibration Input -   46. Controller Input -   48. Controller Output -   50. Calibration Software -   52. Driver Input -   54. Driver Output -   62. Filter Input -   64. Filter Output -   72. Tension Shaft -   74. Drive Shaft -   82. Material Portions -   84. Open Portions -   88. Suction Boxes (a, b) 

1. An optical sensing assembly for detecting media carried by a traveling mesh or suction belt, the belt having material portions that define therebetween open portions, the belt further having a first side and a second side, said optical sensing assembly comprising: an emitter disposed opposite to and spaced a predetermined distance from the first side of the belt, said emitter emitting light in a direction from the first side of the belt toward the second side of the belt; and a detector disposed opposite to and spaced a predetermined distance from the second side of the belt, said detector being disposed in general alignment with said emitter, a detected portion of the light emitted by said emitter passing through the open portions of the belt and being detected by said detector, said detector issuing a detect signal indicative of a reduction in said detected portion of light upon transport of media by said belt between said emitter and said detector.
 2. The optical sensing assembly of claim 1, further comprising filtering means, said filtering means electrically connected to said detector and receiving said detect signal, a media-indicating signal issued by said filter when said detect signal indicates the reduction in said detected portion of light is due to media being disposed between said emitter and said detector.
 3. The optical sensing assembly of claim 2, wherein said filtering means comprises one of a digital, analog, and software-based filter.
 4. The optical sensing assembly of claim 2, wherein said filtering means comprises software filtering.
 5. The optical sensing assembly of claim 2, further comprising: a controller electrically connected with said detector and receiving therefrom said detect signal, a calibration signal issued by said controller; calibration software executed by said controller, said calibration software setting a level of said calibration signal dependent at least in part upon said detect signal; and an emitter driver receiving said calibration signal, said emitter driver being electrically connected to said emitter and issuing thereto an emitter drive signal, said emitter drive signal being dependent at least in part upon said calibration signal.
 6. The optical sensing assembly of claim 1, further comprising a separation distance separating said emitter and said detector, said detector being spaced a predetermined portion of said separation distance from the second side of the belt.
 7. The optical sensing assembly of claim 6, wherein said predetermined portion of said separation distance comprises less than approximately thirty-three percent.
 8. The optical sensing assembly of claim 1, wherein said emitter emits infra-red light and said detector detects infra-red light.
 9. An electrophotographic printing or copying machine, comprising: a traveling suction belt having a first side and a second side, said belt configured for carrying sheets of media, said belt having material portions defining open portions therebetween; and a transmissive optical sensing assembly associated with said belt for detecting at least one of the presence and absence of media upon said belt.
 10. The electrophotographic machine of claim 9, wherein said transmissive optical sensing assembly comprises: an emitter disposed opposite and spaced a predetermined distance from said first side of said belt, said emitter emitting light in a direction from said first side of said belt toward said second side of said belt; and a detector disposed opposite and spaced a predetermined distance from said second side of said belt, said detector disposed in general alignment with said emitter, a detected portion of said light emitted by said emitter passing through said open portions of said belt and being detected by said detector, said detector issuing a detect signal indicative of a reduction in said detected portion of light upon transport of media by said belt between said emitter and said detector.
 11. The electrophotographic machine of claim 10, further comprising filtering means, said filtering means electrically connected to said detector and receiving said detect signal, a media-indicating signal issued by said filter when said reduction in said detected portion of light is due to media being disposed between said emitter and said detector.
 12. The electrophotographic machine of claim 11, wherein said filter comprises one of a digital, analog, and software-based filter.
 13. The electrophotographic machine of claim 11, further comprising: a controller electrically connected with said detector and receiving therefrom said detect signal, a calibration signal issued by said controller; calibration software executed by said controller, said calibration software setting a level of said calibration signal dependent at least in part upon said detect signal; and an emitter driver receiving said calibration signal, said emitter driver being electrically connected to said emitter and issuing thereto an emitter drive signal, said emitter drive signal being dependent at least in part upon said calibration signal.
 14. The electrophotographic machine of claim 11, further comprising a separation distance separating said emitter and said detector, said detector being spaced a predetermined portion of said separation distance from said second side of said belt.
 15. The electrophotographic machine of claim 11, wherein said predetermined portion of said separation distance comprises less than approximately thirty-three percent.
 16. The electrophotographic machine of claim 11, wherein emitter emits infra-red light and said detector detects infra-red light.
 17. A method for detecting the presence or absence of media on a media-carrying mesh or suction belt traveling at a predetermined rate, the belt having material portions that define open portions therebetween, said method comprising: emitting light onto a first side of the belt; receiving on the second side of the belt at least a portion of the emitted light that has passed through the open portions of the belt from the first side to the second side thereof; detecting a reduction in the received portion of light; and filtering the detected reductions in the received portion of light to thereby distinguish between reductions caused by media and reductions caused by material portions of the belt.
 18. The method of claim 17, wherein said emitting step comprises driving an infra-red light emitting diode with a drive signal.
 19. The method of claim 17, wherein said filtering step comprises rejecting reductions in the received portion of light having durations that are less than a predetermined minimum duration.
 20. The method of claim 17, comprising the further step of calibrating the emitting step to emit a level of light that ensures the material portions of the belt do not reduce the received portion of received light by a sufficient amount to be detected while ensuring a sufficient level of light passes through the open portions of the belt to reduce erroneous detections of reductions due to sources other than media on the belt.
 21. A fuser transport assembly, comprising: a traveling suction belt having a first side and a second side, said belt configured for carrying sheets of media, said belt having material portions defining open portions therebetween; and a transmissive optical sensing assembly associated with said belt for detecting at least one of the presence and absence of media upon said belt.
 22. The fuser transport assembly of claim 21, wherein said transmissive optical sensing assembly comprises: an emitter disposed opposite and spaced a predetermined distance from said first side of said belt, said emitter emitting light in a direction from said first side of said belt toward said second side of said belt; and a detector disposed opposite and spaced a predetermined distance from said second side of said belt, said detector disposed in general alignment with said emitter, a detected portion of said light emitted by said emitter passing through said open portions of said belt and being detected by said detector, said detector issuing a detect signal indicative of a reduction in said detected portion of light.
 23. The electrophotographic machine of claim 22, further comprising filtering means, said filtering means electrically connected to said detector and receiving said detect signal, a media-indicating signal issued by said filter when said reduction in said detected portion of light is due to media being disposed between said emitter and said detector. 